Stumped by the Code? Uses Permitted for Metal-Clad ...

c. The insulated conductors under the metallic covering are listed for use in wet locations.

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(12) If single-conductor cables are used, all circuit conductors must be grouped together to minimize induced voltage on the sheath [Sec. 300.3(B)]. Note: Installing the conductors of a circuit close together will minimize the circuit impedance.

(B) Specific Uses.

Informational Note: The “Uses Permitted” isn’t an all-inclusive list, which indicates that other suitable uses are permitted if approved by the authority having jurisdiction (AHJ).

(1) Cable tray. Type MC cable installed in a cable tray in accordance with Art. 392.

(2) Direct buried. Direct-buried cables must be protected in accordance with Sec. 300.5.

(3) Installed as service-entrance cable. Type MC cable is permitted for service entrances when installed in accordance with Sec. 230.43.

(4) Installed outside of buildings. Type MC cable installed outside of buildings must comply with Sec. 225.10, Sec. 396.10, and Sec. 396.12.

Q. What are the uses not permitted by the NEC for metal-clad cable (Type MC)?

A. Type MC cable isn’t permitted to be used where: [330.12]

(1) Subject to physical damage.

(2) Exposed to the destructive corrosive conditions in (a) or (b) [below], unless the metallic sheath or armor is resistant to the conditions, or protected by material resistant to the conditions:

a. Direct burial in the earth or embedded in concrete unless identified for the application.

b. Exposed to cinder fills, strong chlorides, caustic alkalis, or vapors of chlorine or of hydrochloric acids.

Q. What does the Code require when installing metal-clad cable (Type MC) in exposed work?

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A. Exposed runs of Type MC cable must closely follow the surface of the building finish or running boards. Type MC cable installed on the bottom of floor or ceiling joists must be secured at every joist and not be subject to physical damage  [Sec. 330.15].          

PVC coated, sunlight resistant, direct burial rated MC cable can be used in a wet location.

Code Change Summary: A clarification was made to the permitted uses of MC cable installed in a wet location.

The previous code language in 330.10 note (11) was unclear. General use MC cables cannot be used in wet locations but there are some types of specialty MC cables that can. The most common is the PVC coated, sunlight resistant, direct burial listed MC cable in the image.

The revised 2014 code language makes it clear that a corrosion-resistant jacket must be present over the cable and then the 3 conditions apply. Previous wording did not require the corrosion-resistant jacket as a prerequisite to use the 3 conditions.

Below is a preview of the NEC®.  See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).

2011 Code language:

330.10 Uses Permitted.

(11) In wet locations where any of the following conditions are met:

1. The metallic covering is impervious to moisture.
2. A moisture-impervious jacket is provided under the metal covering.
3. The insulated conductors under the metallic covering are listed for use in wet locations, and a corrosion-resistant jacket is provided over the metallic sheath.

2014 Code Language:

330.10 Uses Permitted.

(11) In wet locations where a corrosion-resistant jacket is provided over the metallic covering and any of the following conditions are met:

1. The metallic covering is impervious to moisture.
2. A

   jacket resistant to moisture

   is provided under the metal covering.
3. The insulated conductors under the metallic covering are listed for use in wet

   locations

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